Neutron detectors are used in a variety of different applications. One such application is for well logging tools, in which the characteristics of a subterranean formations are determined by moving the tool along the wellbore of a hydrocarbon (e.g., oil, natural gas, etc.) well. For example, well logging tools may be lowered into a wellbore by “wireline”, or in other configurations the tool may be mounted on a drill collar that is lowered into the wellbore along with the drill bit. Such configurations may be referred to as “logging while drilling” (LWD) or “measurement while drilling” (MWD) systems. The neutron detector may be used to determine a porosity of the subterranean formation at various levels, for example. Other applications in which neutron detectors are used include nuclear reactor instrumentation, material sciences, radiation safety equipment, cosmic ray detection, and the detection of nuclear (i.e., radioactive) materials, for example.
One type of neutron detector is based upon Helium-3 (referred to herein as “3He”). It has a high absorption cross section for thermal neutron beams and is used as a converter gas in neutron detectors. The neutron is converted through a nuclear reaction into charged particles triton (T, 3H) and proton (p, 1H), which are detected.